Features
The SITRANS F Modbus RTU communication complies with the Modbus Serial Line Protocol.
Among other things this implies a master / slave protocol at level 2 of the OSI model. A node (the
master) issues explicit commands to one of the slave nodes and processes responses. Slave
nodes will not transmit data without a request from the master node, and do not communicate
with other slaves.
Modbus is a mono master system, only one master can be connected at a time.
Unicast communication mode
In unicast mode (master/slave mode) the master sends a request to a specific slave device and
waits a specified time for a response.
Master
respo
ns
e
req
uest
Slave
Slave
Slave
Figure 3-1
Unicast Mode
Modbus Frame
The Modbus frame is shown below and is valid for both requests and responses.
Table 3-1
Modbus Frame
SLAVE ADDRESS
FUNCTION MODE
DATA
CRC
1 Byte
1 Byte
0 to 252 Bytes
2 Bytes
References
For further information, please refer to the following specification and guidelines available at
the Modbus Organization (
) website
1. Serial Line Specification & Implementation guide
2. Application Protocol Specification
3.4
Design
The SITRANS FC flowmeters use the Coriolis principle to measure flow and is available in a
compact and a remote design.
Description
3.4 Design
SITRANS MASS 2100 & FC300 (FCT010/DSL)
18
Operating Instructions, 06/2020, A5E39788682-AB